1. Field of the Invention
The present invention relates to an apparatus for cleaning a porous cover of a press roll of a papermaking machine. More particularly, this invention relates to the cleaning of a porous, metallic cover which comes into direct contact with the paper web to be pressed.
2. Information Disclosure Statement
In a typical press section of a papermaking machine, a web to be pressed is supported by a press felt during passage of the web through a press nip. Alternatively, the web is sandwiched between cooperating press felts during passage through a press nip.
Although much research has been carried out in an effort to provide a press felt having a smooth surface, such prior proposals have not proven entirely successful.
In view of the high pressure exerted on the web during passage of the web through the press nip, the textured surface of the press felt tends to mark the surface of the pressed web and imparts to the web a surface which is not smooth.
Ideally, a press felt should have the capability of absorbing water pressed from the web during passage through the press nip. Also, such press felt should have a perfectly smooth surface such that a smooth surface is generated on the resultant pressed web emerging from the press nip.
Porous roll covers have been proposed as substitutes for press felts. However, such prior porous roll covers tend to unduly yield under the extremely high pressures applied to the web at the press nip.
U.S. Pat. No. 3,262,840 to Arthur D. Little issued July 26, 1966 teaches a solid core roll having a porous nylon cover applied thereto. However, not only does the nylon cover tend to yield and creep during passage through the press nip, but also there exists the problem of a buildup of contaminants within the porous cover during use of such porous roll covers.
Also, DE3131083 to Berger et al teaches pumping cleaning fluid through a porous cover but from the inside of the roll outwards. However, such arrangement requires a relatively complex roll structure.
The present invention seeks to overcome both of the aforementioned problems by providing a metallic, porous roll cover which is capable of withstanding the high compressive loads applied at the press nip. Additionally, the present invention provides a simple means for cleaning the porous cover continually during use thereof.
Therefore it is a primary object of the present invention to overcome the aforementioned inadequacies of the prior art proposals and to provide an improved apparatus that makes a significant and substantial contribution to the papermaking art.
Another object of the present invention is the provision of an apparatus for cleaning a porous cover in which a hydrostatic bearing is disposed adjacent to the cover for supporting the press roll, the bearing defining a concave surface which cooperates with the porous cover.
Another object of the present invention is the provision of an apparatus for cleaning a porous cover in which the bearing defines a fluid conveying passageway. The passageway has a first and a second end with the first end being connected to a source of pressurized fluid and the second end being in fluid communication with the concave surface. The apparatus is such that in use of the apparatus when the porous cover of the press roll rotates, fluid passes through the passageway and along the concave surface and between the concave surface and the porous cover so that the pressurized fluid flows inwardly through the porous cover for flushing contaminants lodged within the porous cover outwardly away from the porous cover.
Another object of the present invention is the provision of an apparatus for cleaning a porous cover of a press roll in which the buildup of contaminants on the external surface of the porous cover is inhibited thereby increasing the water-absorbing capabilities of the cover.
Another object of the present invention is the provision of an apparatus for cleaning a porous cover of a press roll in which the pressurized fluid is water.
Another object of the present invention is the provision of an apparatus for cleaning a porous cover in which the pressurized fluid is air.
Another object of the present invention is the provision of an apparatus for cleaning a porous cover of a press roll in which the press roll includes a solid roll core and a porous cover which extends circumferentially around and axially relative to the roll core.
Another object of the present invention is the provision of an apparatus for cleaning a porous cover of a press roll in which the roll cover is metallic.
Another object of the present invention is the provision of an apparatus for cleaning a porous cover of a press roll, the metallic roll cover being hot isostatically pressed onto the roll core (hot isostatic pressing is a powder metallury technique of fabrication).
Another object of the present invention is the provision of an apparatus for cleaning a porous cover of a press roll in which the porous cover is fabricated by a powder metallurgy technique in which the metallic powder particles having a size within the range 50-200 microns are isostatically pressed against the press roll.
Another object of the present invention is the provision of an apparatus for cleaning a porous cover of a press roll in which the metallic powder is of the type known as INCONEL 625.
Another object of the present invention is the provision of an apparatus for cleaning a porous cover of a press roll in which the porous cover is flame-sprayed onto the roll core.
Another object of the present invention is the provision of an apparatus for cleaning a porous cover of a press roll in which the porous cover is ceramic.
Another object of the present invention is the provision of an apparatus for cleaning a porous cover of a press roll in which the external surface of the porous cover is machined to define a smooth, cylindrical surface thereon for direct contact with a paper web to be pressed.
Another object of the present invention is the provision of a method for cleaning a porous cover of a press roll in which the press roll is hydrostatically supported on a hydrostatic bearing and pressurized fluid is injected through the external surface of the porous cover for flushing contaminants within the porous cover outwardly away from the porous cover thereby inhibiting the buildup of contaminants on the external surface of the porous cover.
Other objects and advantages of the present invention will be apparent to those skilled in the art by a consideration of the detailed description contained hereinafter taken in conjunction with the annexed drawings which show a preferred embodiment of the present invention.